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Full text of "Grand Tower limestone (Devonian) of southern Illinois"

STATE OF ILLINOIS 

DEPARTMENT OF REGISTRATION AND EDUCATION 




GRAND TOWER LIMESTONE 
(DEVONIAN) OF 
SOUTHERN ILLINOIS 



Wayne F. Meents 
David H. Swann 



ILLINOIS STATE GEOLOGICAL SURVEY 

John C. Frye, Chief URBANA 



CIRCULAR 389 



1965 



Digitized by the Internet Archive 

in 2012 with funding from 

University of Illinois Urbana-Champaign 



http://archive.org/details/grandtowerlimest389meen 



GRAND TOWER LIMESTONE 
(DEVONIAN) OF SOUTHERN ILLINOIS 

Wayne F. Meents and David H. Swann 



ABSTRACT 

The Grand Tower Limestone has been the source of over 
a hundred million barrels of oil in Illinois, the bulk of the Devo- 
nian production of the state. The formation underlies most of 
southern and central Illinois and extends into Missouri, Iowa, 
Indiana, and Kentucky, where its equivalents are the Cooper, 
Wapsipinicon, and Jeffersonville Limestones. The Grand Tower 
has a maximum thickness of a little more than 200 feet. It is a 
sandy, but otherwise pure, carbonate unit that forms approxi- 
mately the lower half of the Middle Devonian carbonate sequence 
of the region. TheGrand Tower is dominantly fossiliferous lime- 
stone in southern Illinois, dolomite in most of central Illinois, 
and lithographic limestone where it pinches out in north-central 
Illinois against the Sangamon Arch. The Sangamon Arch was an 
east-west structure that probably separated the Grand Tower from 
the Wapsipinicon Limestone of northern Illinois and Iowa during 
their deposition. Ithasbeen so modified by post-Devonian move- 
ments that it is no longer an important structural element. 

TheGrand Tower is thin or lacking over much of the Sparta 
Shelf, the western shelf of the Illinois Basin. The type sections 
of the Grand Tower and of several other Devonian formations lie 
in the Wittenberg Trough, a partially fault-bounded trench be- 
tween the Sparta Shelf and the main body of the Ozarks. The 
Wittenberg Trough was active during Devonian and perhaps the 
early part of Mississippian time but largely has been destroyed 
as a structure by subsequent movements. 

The three members and one bed formally recognized in 
the Grand Tower occupy limited areas, so that the bulk of the for- 
mation is not differentiated. The Dutch Creek Sandstone Mem- 
ber is a discontinuous but widely distributed basal unit. The 
Geneva Dolomite Member is a dark brown unit near the base of 
the formation. It extends into central Illinois from Indiana but 
does not cross the state. The Cooper Limestone Member is a 



ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 

lithographic limestone that lies at the top of the formation im- 
mediately south of the Sangamon Arch . It extends from Missouri 
into north -central Illinois. The Tioga Bentonite Bed is an altered 
volcanic ash that extends from the Appalachian Basin into parts 
of the Illinois Basin where it is only a few inches thick. It lies 
6 to 15 feet below the top of the Grand Tower. 

The Grand Tower is nearly everywhere overlain by the 
Lingle Limestone and correlative units of Hamilton (late Middle 
Devonian) age with, at most, a slight disconformity. The Grand 
Tower unconformably overlies many formations of Lower Devo- 
nian, Silurian, and Ordovician age. 

The oil of the Grand Tower largely has been produced from 
the Geneva and other dolomite units . In recent years the Dutch 
Creek Sandstone Member has been found to contain oil in the 
deepest part of the Illinois Basin at depths greater than 5000 
feet. The Dutch Creek is potentially productive over a large 
area in extreme southern and southeastern Illinois. 

The cross sections in the report illustrate zonation and 
changes in the New Albany Shale Group of Upper Devonian and 
Kinderhookian (lower Mississippian) age, which overlies the 
Lingle Limestone. The lowest unit in the New Albany in eastern 
Illinois, the Blocher Shale, grades laterally into the Alto Lime- 
stone of western Illinois. 



INTRODUCTION 

The Grand Tower Limestone forms approximately the lower half of the Middle 
Devonian carbonate sequence of southern and central Illinois (fig. 1). It is a rel- 
atively pure carbonate unit that is commonly 50 to 150 feet thick. It is dominantly 
fossiliferous limestone in southern Illinois and dolomite in much of the central 
part of the state. It is lithographic limestone in the northern part of central Illinois 
where it pinches out against the Sangamon Arch. 

In southern Illinois it generally lies on a very cherty carbonate unit, the 
Clear Creek Limestone, the top formation of the Lower Devonian. The Grand Tower 
overlaps the Clear Creek and older Devonian formations to lie upon the Silurian in 
much of central Illinois. The Grand Tower is generally overlain by the Lingle Lime- 
stone, a darker more argillaceous limestone that forms the upper half of the Middle 
Devonian sequence. 

The Grand Tower is nearly free of silt and clay but is somewhat sandy. 
Sand is concentrated near the base; it occurs as floating grains in limestone or 
dolomite in some areas but as beds of sandstone in others. The basal sandstone 
is the Dutch Creek Sandstone Member. It is generally only a few inches or a few 
feet thick and is discontinuous. In many localities the lower beds of the Grand 
Tower carry little or no sand, but regions without sandstone are not large, and the 
Dutch Creek is recognized in all parts of the Illinois Basin where Grand Tower 
sediments are represented. 

In central Illinois the Grand Tower is largely dolomite, and the lower part 
of the formation is a dark brown unit, the Geneva Dolomite Member. The Geneva 
extends in a broad arcuate band, convex to the north, from the outcrop in south- 



GRAND TOWER LIMESTONE 




Figure 1 - Distribution of the Grand Tower Limestone and correlative limestone 
formations in the Illinois Basin region shown in relation to major 
structures. The age of the deposits truncating the Grand Tower at its 
margins is shown by the letters Q = Quaternary, K = Cretaceous, 
P = Pennsylvanian, M = Mississippian and Upper Devonian. Compiled 
from new data with the aid of William G. North, from literature cited 
in the report, from published state geologic maps, and from Branson 
(1923 and 1944), Freeman (195 1), Grohskopf, Hinchey, and Greene 
(1939), Pinsak and Shaver (1964), Ross (1963), and Wilson (1949). 



1 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 

central Indiana into eastern and central Illinois but does not reach across the state. 
It is overlain by a somewhat thicker sequence of lighter colored dolomites that are 
also placed in the Grand Tower Formation. In many localities the Dutch Creek 
occurs at the base of the Geneva, but elsewhere there is little sand, and the 
Geneva rests directly upon pre-Grand Tower units. 

A zone dominated by lithographic limestone occurs at the top of the Grand 
Tower in the northern and western parts of central Illinois. The lithographic unit 
grades southeastward into the light-colored dolomite of the upper part of the Grand 
Tower, but northward and westward it overlaps these dolomites and is the only part 
of the Grand Tower to reach the outcrops in Calhoun County, Illinois, and adjacent 
Missouri. It has generally been correlated with the Wapsipinicon Limestone in 
the subsurface of western Illinois, but it is identicalin lithology with the unit 
commonly called Cooper in outcrops in northern Missouri and is here recognized 
as the Cooper Limestone Member of the Grand Tower. The name Wapsipinicon is 
restricted to the limestone north of the Sangamon Arch. The Cooper Member under- 
lies the Lingle Limestone or equivalent strata in the Cedar Valley or Callaway Lime- 
stones. At the east it overlies other units in the Grand Tower, but westward it 
overlaps these to lie on various Silurian or Ordovician formations. 

A thin bed of altered volcanic ash, the Tioga Bentonite Bed, occurs in sev- 
eral counties in the eastern part of Illinois near the top of the Grand Tower (fig. 1) . 
It is the thin western edge of a volcanic ash fall that blanketed the eastern states. 
It has not been traced to western Illinois, and its position with respect to the 
Cooper Member is not known. 

The Geneva Member and overlying dolomite beds in the Grand Tower have 
been the most prolific oil pay zones in the Devonian of Illinois and Indiana. The 
Dutch Creek Sandstone Member carries oil in the deep part of the Illinois Basin in 
southern Illinois. The production is from depths below 5000 feet, the deepest yet 
found in the Illinois Basin. 



STRATIGRAPHY 

Grand Tower Limestone 

The Grand Tower Limestone was named by Keyes (1894) for Grand Tower, 
Illinois, where the formation is well exposed along the Mississippi River north of 
the town in two hills known as the Bake Oven and the Backbone (fig 2). 

At the Bake Oven, the formation is 157 feet thick and has been completely 
exposed during some extremely low river stages. The lower 15 to 25 feet is com- 
monly beneath water and is covered by river silt during some low stages. Keyes' 
original usage is identical to that of the present report. His Grand Tower Limestone 
consisted of the section above the Clear Creek Limestone and beneath the dark, 
shaly limestone (with Hamilton fossils) that he included in his Callaway Limestone 
but which is now assigned to the Lingle Limestone in southwestern Illinois and to 
the Beauvais Sandstone and the St. Laurent Limestone in southeastern Missouri. 
Ulrich, in Buckley and Buehler (1904, p. 109-111), revised the Grand Tower to 
include the younger beds now assigned to the Lingle Limestone and its equivalents. 
Savage (1910, p. 116) restored the original limits to the Grand Tower, although he 
believed that by excluding the Clear Creek Formation he was emending rather than 
following Keyes. He was apparently unaware of the original reference and misread 



LINGLE 



DUTCH 

CREEK 

MBR. 



clear\ 

CREEK . 






23 



Limestone, brownish gray, argillaceous, thin 

bedded, base is zone of Microcyclus found in Backbone 



nzj 



/ 



»■ 



IP 



■:i: 



;$-. 



Limestone, 
massive; 



Limestone, 
mossive; 



brownish gray, lithographic, 
lower 4 feet cherty 



brownish gray, lithographic, 
upper 9 inches thin bedded 



ji/j Limestone, bluish gray, argillaceous, Chonetes abundant 



Limestone, pinkish brown, lithographic, 
thin bedded with shaly partings; upper 
2 '/2 feet cherty 



2 '/2 1 Limestone, light gray, very fine grained 



Limestone, brownish gray, fine grained, uniform in 
8'A texture, thin bedded, little chert at base 



.\. 1 Limestone, brownish gray, medium crinoid calcarenite; locally 

conglomeratic at base with chert and phosphate groins 
.\. 1 Limestone, brownish gray, lithographic, 
buff-gray chert at bottom 



6'/6 



, Limestone, brownish gray, very fine crinoid calcarenite 



, Limestone, dark brownish gray, lithographic 
4/6 thin bedded; tan chert at base 



■ 9 '/2 



Limestone, brownish gray, very fine crinoid colcarenite 
thick bedded 



Limestone, brownish gray, medium crinoid calcorenite 
prominent cherl zone forms reentrant 
in Bake Oven C 

Limestone, brownish gray, medium crinoid 
cclcdrenite, massive 

Limestone, brownish gray, fine grained, mottled 



i. 1 Limestone, brownish gray, 
' numerous fucoids, bract 



fine calcarenite, 
chiopods, and corals 



Limestone, light gray, medium to coarse 
crinoid calcarenite, massive-, sandy dnd 
strongly cross bedded in lower half; 
indistinctly cross bedded in upper half 
with ripple marks and wavy beds 



38 



Limestone, light gray, medium to coarse 
sandy; interbedded with light 
I I /2 gray calcareous sandstone 




Sandstone, light gray, very 
calcareous, cross bedded, 
12 friable; conglomeratic in 

lower bed 



Fine fraction = clay ond fine silt 
Coarse froction > cloy ond fine silt 
IO 



_l_ 



30 

_1_ 



20 

_1_ 



PERCENT INSOLUBLE RESIDUE 



| / I imestnne light gray, calcarenitic; 
^a ") interbedded with light gray chert 



Figure 2 - Type section of the Grand Tower Limestone in the Bake Oven and Back- 
bone hills, north of Grand Tower, near the center of the Ej sec. 23, 
T. 10 S., R. 4 W., Jackson County. Compiled and described by Charles 
W. Collinson, incorporating insoluble residue analyses from a study by 
Hallstein (1952). 



5 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 

a later vague statement by Keyes (1895, p. 339) which, unlike the original, did 
not specifically exclude the Clear Creek from the Grand Tower. 

The Grand Tower is recognized throughout southern Illinois. It extends 
eastward into Indiana where it is called the Jeffersonville Limestone. The lower 
part of the Grand Tower is overlapped eastward, so that the base of the Jefferson- 
ville at its type outcrop on the Ohio River in south-central Indiana is younger than 
it is in the subsurface at the Indiana -Illinois border, and probably younger than 
the base of the Grand Tower outcrops in southwestern Illinois. 

The Grand Tower extends northward in Illinois to a pinch -out on the south 
flank of the Sangamon Arch (fig. 1). The Sangamon Arch was a structural uplift 
trending slightly north of east that crossed central Illinois during Devonian depo- 
sition. It has been downwarped since then until it is not a present-day arch 
(Whiting and Stevenson, 1965). It is recognized by stratigraphic relations. 

Strata north of the Sangamon Arch essentially equivalent to the Grand Tower 
are assigned to the Wapsipinicon Limestone. Although the name Wapsipinicon was 
formerly used south of the Sangamon Arch (Lowenstam, 1948, p. 162-164; Workman, 
1944, p 195, 197), there is no natural boundary to separate the Grand Tower from 
the Wapsipinicon south of the 50 to 80 mile gap at the Sangamon Arch. The beds 
in Illinois north of the arch extend continuously to the outcrops along the Wapsipi- 
nicon and Cedar Rivers in Iowa (fig. 1). 

Other aspects of the regional correlations have been discussed by Cooper 
etal. (1942), Cooper (1944), Croneis (1944), Savage (1920a, 1920b), and We Her 
(1944). 

Dutch Creek Sandstone Member 

A basal sandstone or sandy limestone unit was mentioned by all of the 
early writers, both before and after the formal naming of the Grand Tower Limestone. 
Except for early reference to the Oriskany Sandstone of New York (Worthen, 1866, 
p. 124), this arenaceous unit was described as the basal member but not named 
by the early writers. Savage (1920, p. 175) named it the Dutch Creek Sandstone 
and gave it formational rank, thus separating it from the Grand Tower. Savage's 
classification has been followed since 1920, although the gradational nature of 
the Dutch Creek-Grand Tower contact and the occurrence of the sandstone in iso- 
lated bodies has been commonly noted. In the present paper the Dutch Creek is 
recognized as a discontinuous basal member of the Grand Tower Limestone rather 
than as a distinct formation. Because sandy limestone occurs throughout the Grand 
Tower, the name Dutch Creek is used only where beds of sandstone are present. 

The Dutch Creek Sandstone was named for unspecified exposures along 
Dutch Creek, a tributary of Clear Creek, which flows northwest in central Union 
County 3 or 4 miles west of Jonesboro. Few, if any, sandstone outcrops occur 
along and near the bed of the main stream, but loose float is present on the valley 
walls and in the stream bed. Poor outcrops can be found along some hill slopes 
and in the beds of several tributaries. The contacts of the Dutch Creek are obscure 
in most exposures because of solution of the carbonates immediately above and 
below the sandstone. A sharp contact with the underlying Clear Creek and a gra- 
dational one with the main body of the Grand Tower are well shown north of Clear 
Creek along a secondary road about 1. 1 miles northwest of its junction with Illinois 
highway 127, in the center of the w| NW| sec. 27, T. US., R. 2 W., Union 
County, Cobden Quadrangle, Other important Dutch Creek outcrops are listed by 
Weller and Ekblaw (1940). 



GRAND TOWER LIMESTONE 7 

Geneva Dolomite Member 

The Geneva Dolomite, named for a town in southeastern Shelby County, Indi- 
ana (Collett, 1882, p. 63, 81-82), is a dark brown, crystalline dolomite that reaches 
the surface only in the northern and central parts of the Devonian outcrop belt in 
southern Indiana, where it underlies the Middle Devonian Jeffersonville Limestone 
and unconformably overlies Silurian strata. In the subsurface it extends westward in 
a belt that arches gently to the north and crosses west-central Indiana (Bieberman, 
1949) and central Illinois (Schwalb, 1955) but does not reach the west side of the 
Illinois Basin. Controversy has arisen concerning the nature of the surface separ- 
ating the Geneva from the Jeffersonville in the Indiana outcrop area and the presence 
or absence of lateral gradation between the two. In the subsurface of Illinois the 
Geneva is a facie s that grades laterally into the lower part of the Grand Tower Lime- 
stone. It is considered a member of the Grand Tower in Illinois. The Dutch Creek 
Sandstone Member is present in patches at the base of the Geneva Dolomite Member 
just as it is at the base of the limestone facies of the Grand Tower farther south. 
The Geneva is overlain by undifferentiated limestone and dolomite units of the Grand 
Tower. 

Cooper Limestone Member 

An unfossiliferous to poorly fossiliferous limestone that crops out in patches 
in Cooper and other counties in north-central Missouri was named the Cooper Mar- 
ble (now Limestone) by Swallow (1855, p. 108, 196). In its type section it is the 
only Devonian unit exposed. In some other outcrops it is overlain by a darker, 
shalier, much more fossiliferous limestone that is equivalent to the Lingle and 
was named the Callaway Limestone by Keyes (1894, p. 43). The Cooper has gen- 
erally been placed beneath the Callaway as a distinct, separate formation, but 
Unklesbay (1952, p. 30-31) considered it a gradational unit within the Callaway 
and designated it the Cooper Facies of the Callaway Limestone. 

The Cooper occurs in the northern and central part of the Devonian outcrop 
belt in Calhoun County, Illinois (Rubey, 1952, p. 31), where it is a lens of rela- 
tively dense, light colored, pure limestone forming the basal few feet of the Cedar 
Valley Limestone. A few feet of light gray to light brownish gray, extra finely 
crystalline to lithographic, unfossiliferous limestone that contains small tubes or 
"bird's-eyes" of clear calcite is exposed on the west bank of the Illinois River, 
1.5 miles south of the bridge at Hardin, at the center of the west line of the SW-| 
sec. 35, T. 10 S., R. 2 W., Calhoun County, Hardin Quadrangle . This outcrop 
is typical of the Cooper. Several hundred feet to the southwest these beds are 
overlain by 15 to 18 feet of medium to dark brownish gray, shale -streaked, fossil- 
iferous limestone that was formerly classified as Cedar Valley (Cooper and Cloud, 
1938; Rubey, 1952) but that is here assigned to the Lingle Formation, although 
still correlated with the Cedar Valley. 

East of the Illinois River the Cooper occurs in the subsurface in a belt 60 
to 90 miles wide extending eastward across the state just south of the Sangamon 
Arch. The Cooper generally rests on Ordovician rocks in Missouri but on Silurian 
rocks, or other parts of the Grand Tower, in Illinois. On its north margin the 
Cooper is overlapped by the Lingle. On the south it grades laterally into the light- 
colored dolomites that form the upper part of the Grand Tower above the Geneva 
Member. The contact between lithographic limestone to the north or northwest and 
dolomite to the south or southeast rises stratigraphically so that the highest, young- 
est bed of the Cooper extends farthest south to the limit shown on figure 3. 



ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 




Figure 3 - Thickness and facies of the Grand Tower Limestone in southern Illinois 



GRAND TOWER LIMESTONE 




Sandstone, mostly 
porous, at base 

No sand at base 



showing lines of cross sections A-A' (fig. 4), B-B' (fig. 5), and C-C (fig. 6). 



10 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 

Because of its gradation with the upper part of the dolomitic facies of the 
Grand Tower Limestone, the lithographic limestone unit is classified in Illinois as 
the Cooper Limestone Member of the Grand Tower Limestone. The unit was former- 
ly assigned to the Wapsipinicon Limestone (Workman, 1940; Lowenstam, 1948) in 
the subsurface of Illinois and to the Cedar Valley Limestone in the Calhoun County 
outcrops. The name Wapsipinicon will be used only north of the Sangamon Arch. 

Although Cooper strata in many ways resemble those of the Wapsipinicon, 
they tend to be more fossiliferous, they do not include anhydrite or gypsum, and 
they are probably less brecciated than certain beds in the Wapsipinicon. The maxi- 
mum thickness of the Cooper in Illinois is about 60 feet. 

Tioga Bentonite Bed 

Although the presence of a thin bed of bentonite, altered volcanic ash, 
near the top of the Grand Tower and the Jeffersonville in Illinois and Indiana was 
known by 1940, it has not been noted in the literature. The bentonite is generally 
no more than 1 or 2 inches thick. It locally becomes 6 or 8 inches thick in the 
Illinois Basin but is much thicker in the Appalachian Basin. Its presence there was 
noted by Fettke (1931) who later (in Ebright, Fettke, and Ingham, 1949) named it 
the Tioga Bentonite Bed because of its usefulness as a subsurface stratigraphic 
marker in the Tioga Gas Field, Tioga County, Pennsylvania. The distribution and 
thickness of the Tioga Bentonite in the Appalachian region as reported by Fettke 
(1952), Flowers (1952), Oliver (1954, 1956), and Dennison (1961) led Dennison 
to conclude that the bed consists of ash ejected from a volcano located near Lex- 
ington, Virginia. 

In the Illinois Basin the bed generally occurs 6 to 15 feet beneath the top 
of the Grand Tower or the top of the Jeffersonville. It has been found in many wells 
in southwestern Indiana and eastern Illinois and is probably present throughout the 
area indicated on figure 1, although its thinness precludes its recognition in all 
wells. Its distribution is traced most readily on geophysical logs (fig. 6), because 
its physical attributes contrast sharply with those of the dolomite or limestone in 
which it occurs. It is probably 1 to 4 inches thick in the majority of wells in which 
it has been noted on electric logs. However, it is at least 8 inches thick in south- 
ern Sullivan County, Indiana, and it has been identified on some sonic logs where 
it is probably no more than ^-inch thick. 

In samples, the bentonite is represented by rounded, somewhat blocky chips 
of greenish gray to brownish gray shale containing small flakes of brown biotite 
that distinguish it from normal Devonian shale. Its color differs only slightly from 
the medium gray to brownish gray of normal detrital shales. However, the abundant 
mixed-layer clay mineral that characterizes metabentonite or K-bentonite is shown 
by the X-ray spectrograph and differs sharply from the illite -quartz suite of the nor- 
mal shales. 

The Tioga has not been recognized in wells in the southwestern part of the 
state, nor in outcrops of the Grand Tower in southwestern Illinois and southeastern 
Missouri. It occurs about 4 or 5 feet above the base of the Wapsipinicon Limestone, 
If feet below the top of the basal Coggin Dolomite Member in the Central City quar- 
ry, on the north bank of the Wapsipinicon River, northwest of Central City, in the 
SEi sec. 28, T. 86 N., R. 6 W., Linn County, Iowa. The relation of the Tioga Bed 
to the Cooper Member in western Illinois and adjacent Missouri is not known. Its 
position in Iowa suggests that it may lie near the base of the Cooper where the 
Cooper is best developed. 



GRAND TOWER FORMATION 11 



Formations Above the Grand Tower Limestone 

Figures 4 through 6 illustrate the character and stratigraphic relations of 
the Lingle Limestone, the Alto Limestone, and units in the New Albany Shale Group, 
as well as those of the Grand Tower. Figure 4 shows that the unit called Alto Lime- 
stone in western Illinois (west of well No. 8 in eastern Jefferson County) grades 
laterally into the Blocher Shale of the New Albany Shale Group in eastern Illinois. 
The top of Devonian Limestone (top of Hunton Limestone Megagroup) is at the top 
of the Alto in the western region but at the base of the Blocher in the eastern re- 
gion. In the vicinity of well No. 8, the surface that is used to separate the New 
Albany Shale Group from the Hunton Limestone Megagroup has an abrupt cutoff 
or step-down to the east of about 30 feet. 



DISTRIBUTION AND THICKNESS 

The thickness in southern Illinois of the entire Grand Tower Limestone, 
including its members, is shown on figure 3. The thickness in the central and 
west-central parts of the state is shown by Whiting and Stevenson (1965). The 
regional distribution of the Grand Tower and its correlatives with regard to major 
structural features is shown on figure 1. 

Sparta Shelf 

The Grand Tower is absent in a large area in southwestern Illinois, includ- 
ing most of St. Clair, Monroe, Randolph, Washington, Perry, and Jackson Counties . 
The region in which it is absent or thin corresponds roughly to the western shelf 
of the Illinois Basin, a feature here named the Sparta Shelf (fig. 1) after the town 
in Randolph County. The Sparta Shelf lies between the Fairfield Basin, the larger 
and more northerly deep depression of the Illinois Basin, and the main body of the 
Ozarks. On the east it is sharply differentiated from the Fairfield Basin by the 
DuQuoin Monocline. On the southwest it is sharply differentiated from the Ozarks 
by the Ste. Genevieve Fault System and the feature later described as the Witten- 
berg Trough. Its limits on the north are indefinite. The Sparta Shelf expands 
northward into the broad northwestern flank of the Illinois Basin that lies between 
the Fairfield Basin and the Mississippi River Arch but is sharply differentiated 
from neither. In earlier discussions of Silurian, Devonian, and lower Mississip- 
pian stratigraphy, the Sparta Shelf was referred to as the eastern lobe of the Ozarks, 
eastern extension of the Ozarks, or the area with little or no sediments (Lowen- 
stam, 1948; Workman, 1944; Workman and Gillette, 1956). 

The Grand Tower is overlapped on the Sparta Shelf by the overlying Lingle 
Limestone (fig. 4). The Lingle in turn is overlapped by younger units that rest on 
progressively older pre -Grand Tower formations farther west. At the west edge of 
the shelf, Valmeyeran (Middle Mississippian) rocks lie on the Silurian or Ordovi- 
cian. 

Eastward from its feather edge, the Grand Tower thickens across the Fair- 
field Basin to 140 to 200 feet (figs. 3, 4, and 6). It is thickest near the Illinois- 
Indiana boundary. Farther east the Geneva Dolomite and the Jeffersonville Lime- 
stone, which are equivalent to the Grand Tower, thin gradually across the eastern 
shelf of the Illinois Basin. At the Indiana outcrop they are only half as thick as at 
the state line. The eastward thinning is more abrupt in Kentucky, where the Jeffer- 



12 



ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 




Figure 4 - East-west electric log cross section of the Grand Tower and associated 
See Appendix for list of wells. 

sonville is generally overlapped in the subsurface west of the outcrop belt. A few 
thin scattered outliers of equivalent strata in west-central Tennessee have been 
included in the lower part of the Pegram Limestone (Lingle equivalent). 

The Grand Tower occurs in central western Illinois in a broad belt that 
crosses the north part of the Sparta Shelf south of the Sangamon Arch (figs. 1 and 
5). In this region the formation is thinner than it is in the Fairfield Basin. Iso- 
lated patches of equivalent strata as much as 30 feet thick continue this belt west- 
ward halfway across Missouri. 



Wittenberg Trough 

A striking feature of the distribution of the Grand Tower Limestone is the 
narrow tongue or series of isolated blocks that extend northwestward from central 



GRAND TOWER LIMESTONE 



13 




{continued next page) 



units from Washington County, Illinois, to Union County, Kentucky (on four pages), 



Union County in southwestern Illinois into Ste. Genevieve County, Missouri. The 
structural trough in which this tongue of the Grand Tower was deposited, and which 
is largely responsible for its preservation, is here named the Wittenberg Trough 
(figs. 1 and 3). The Wittenberg Trough developed largely during the Devonian, 
and by early Mississippian time was a structural trench 70 miles long, 1 to 10 
miles wide, and 100 to more than 1000 feet deep that broke the simple structural 
slope between the Ozarks and the Illinois Basin. Post-Mississippian movement 
has distorted and partially destroyed the Wittenberg Trough. The northwest end 
has been tilted up. The structural displacement has been increased along most of 
the southwest side, the edge toward the Ozarks, whereas it has been decreased 
or even eliminated on the northeast or basin side. 



14 



ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 




Figure 4 - 



The trough is shown on the geologic map by the Ordovician outlier in the 
Weingarten Graben in western Ste. Genevieve County; by the Devonian and Siluri- 
an grabens in southern Ste. Genevieve County; by the upper Mississippian of east- 
ern Perry County, Missouri; by the Pennsylvanian outlier at Fountain Bluff, in 
southwestern Jackson County, Illinois; and by the structurally controlled course 
of the Mississippi Valley from Ste. Genevieve to Grand Tower. Although the Wit- 
tenberg Trough is now largely outlined by faults, its margin included monoclinal 
flexures so that the term graben would not be appropriate. 



GRAND TOWER LIMESTONE 



15 




The western end of 
the structure was described 
by Weller and St. Clair (1928) 
in their discussion of fault- 
ing in Ste. Genevieve Coun- 
ty. At the eastern end puz- 
zling contradictions in fa- 
des and thickness of out- 
cropping Devonian units in 
different parts of Jackson 
and Union Counties, Illinois, 
have long been noted, but 
subsurface information was 
needed to complete the pic- 
ture . Although well control 
is still very sparse, the 
Wittenberg Trough appears 
to merge at its eastern end 
into the southern part of the 
Illinois Basin and to be in 
effect the westernmost ex- 
tension of the southern deep 
of the basin, the Moorman 
Syncline „ 

The Wittenberg Trough 
affected not only Grand Tower 
sedimentation, but that of 
other Devonian formations „ 
In it were deposited the 
thickest Lower Devonian 
sections of the Midwest as 
well as the thickest Middle 
Devonian outside the Michi- 
gan Basin. During the De- 
vonian, the axis of the Wit- 
tenberg Trough may have 
migrated slightly northward, 
because the thickest sections 
of the Clear Creek apparently 
lie 2 to 6 miles southwest 
of the thick sections of the 
Grand Tower, Lingle, Alto, 
and New Albany. 
The outcrops of thick Grand Tower Limestone lie in fault blocks and tilted 
sections on the downthrown northeastern side of the major faults of the Ste. Gene- 
vieve -Rattlesnake Ferry system. These faults are largely post-Mississippian and, 
at least in part, post-Pennsylvanian. They now outline the southwest edge of the 
Wittenberg Trough, although they appear to lie somewhat north of the original edge 
of the trough. The Grand Tower Limestone does not descend into the basin from 



Continued. 



16 



ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 




Figure 5 - Northwest-southeast electric log cross section of the Grand Tower Limestone 
See Appendix for list of wells. 

these outcrops but is cut off abruptly within 1 to 6 miles by pre-Mississippian 
faults and corresponding monoclines that are down to the southwest toward the 
Ozarks. These mark the edge of the extensive area of the Sparta Shelf over which 
the Grand Tower is lacking. Although the Lingle, Alto, and New Albany overlap 
the Grand Tower on the Sparta Shelf, they, too, are gone at the southwest edge 
next to the Wittenberg Trough. Within the trough the Grand Tower is 100 to 200 
feet thick and is overlain by 200 to 300 feet of Lingle and Alto and by to 100 feet 
of New Albany. The type section of the Grand Tower (fig. 2) is typical of the sec- 
tions in this region. The Grand Tower is absent south of the western end of the 
Wittenberg Trough where the Ordovician rocks of the Ozarks are found immediately 
south of the bounding faults. In Illinois, south of the eastern end of the trough, 
the formation thins rapidly. Limestone disappears and only a few feet of the Dutch 
Creek Sandstone Member is left 5 miles beyond the axis of the trough. 



Dutch Creek Sandstone 

The Dutch Creek Sandstone averages about 15 feet thick at the outcrops in 
Union and Jackson Counties, Illinois. As much as 35 feet has been reported at 
poorly exposed outcrops where much of the section, before leaching, may have 
consisted of sandy limestone. In extreme southern Illinois, south of the area shown 
on figure 3, several wells have 10 to 15 feet of good sandstone. In the patterned 
area on figure 3 the maximum thickness approaches 15 feet, but many wells have 
only 1 or 2 feet of permeable sandstone, and the average for the area is probably 
no more than 4 or 5 feet. In east-central Illinois, north of the mapped area, both 



GRAND TOWER LIMESTONE 



17 




Icon/muea next pogel 



and associated units from Macoupin County to Wayne County (on three pages). 

the average and maximum thicknesses appear to increase so that as much as 20 
feet of sandstone has been recorded in Edgar and Douglas Counties, although some 
wells in these counties have no sandstone. 



STRATIGRAPHIC RELATIONS 



Upper Contact 

The Grand Tower Limestone is everywhere overlain by the Lingle Limestone 
in the area mapped in detail on figure 3. In general, there is a slight disconform- 
ity above the thinner sections in the western part of the area and an apparent con- 
formity in the east over the thicker sections in the Fairfield Basin. In the west, 
the basal beds of the Lingle Limestone tend to be quite sandy, and a basal sand- 
stone member equivalent to the Beauvais Sandstone of Missouri is present in many 
localities. In cores the contact is sharp and in many cases uneven. However, 
truncation of the upper part of the Grand Tower is limited because the Lingle rests 
on the same bed over large areas. The westward thinning of the Grand Tower re- 
sults more from internal thinning and from overstep at the base than from pre-Lingle 
truncation at the top. 

Regionally, too, the Grand Tower and equivalent strata are generally over- 
lain and overlapped by the Lingle or other carbonate formations of late Middle De- 
vonian (Hamilton) age (fig. 1). There are a few exceptions. The feather edges of 
Grand Tower and Lingle on the south side of the Sangamon Arch approach each other 
in Christian County where the New Albany Shale in some wells is underlain by a 



18 



ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 




Figure 5 - Continued. 

few feet of Middle Devonian limestone that might belong to either formation. North 
of the arch the Wapsipinicon Limestone, the equivalent of the Grand Tower, is 
directly overlain by the New Albany over a few square miles in Adams County (Whit- 
ing and Stevenson, 1965). In Iowa and northeastern Missouri, limestone equiva- 
lent to the Lingle overlies the Grand Tower equivalents, but in three or four counties 
in north -central Missouri, Lingle equivalents are overlapped by thin sandstones of 
Kinderhookian (Lower Mississippian) and Upper Devonian age, which lie directly 
on the Cooper, the representative of the Grand Tower. In west-central Tennessee, 
some remnants of the Middle Devonian Pegram Limestone beneath the black shale 
have been variously equated to the Grand Tower and the Lingle. Most, if not all, 
Pegram outcrops include beds of Hamilton (Lingle age) so that areas where the 
Grand Tower equivalents are overlain by the Chattanooga (New Albany) must be 
small. Thus, the Grand Tower is nearly everywhere overlain by Lingle, except 
where both formations or their equivalents are beveled along the edges of the basin 
by pre-Pennsylvanian, pre -Cretaceous, or pre -Quaternary erosion (fig. 1). 

Lower Contact 



In contrast to its conformable or nearly conformable upper surface, the lower 
surface of the Grand Tower is one of the major unconformities of the Midwest. In 



GRAND TOWER FORMATION 



19 




Figure 6 - North-south cross section of the Grand Tower and associated units from 
Gallatin County to Lawrence County. See Appendix for list of wells. 



20 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 

the eastern and southern parts of the area mapped on figure 3, the Grand Tower lies 
on the Clear Creek Limestone. The relation is generally unconformable, although 
the time interval separating the two formations could not have been very great. The 
contact is abrupt. At a single outcrop in Union County, the typical Clear Creek 
and Dutch Creek lithologies have been reported to be interbedded, but minor fault- 
ing and slumping at this locality obscures the true relation, and the contact is 
probably simple and abrupt. In the subsurface, too, the contact has been sharp 
in all cored wells, and reports of intergrading or interbedding seem restricted to 
studies of relatively inferior sample sets. 

The base of the Grand Tower truncates the pre -Clear Creek Devonian forma- 
tions in a belt that crosses Clinton, Marion, Fayette, Effingham, and Shelby Coun- 
ties. Farther northwest the Grand Tower lies on Silurian dolomites that are of Ni- 
agaran age within the area of figure 3. Beyond the limits of the map, the Grand 
Tower overlaps the Niagaran to lie on Alexandrian (Lower Silurian) and Ordovician 
rocks. The situation is similar north and east of the mapped area in central Illinois 
and in Indiana, where the Grand Tower and its equivalents overlap the Lower De- 
vonian and rest on the Silurian. To the southeast, in central Kentucky, the trunca- 
tion extends down to the Ordovician. 

Considering its regional truncation, the surface upon which the Grand Tow- 
er was deposited appears astonishingly smooth. The other major unconformable 
surfaces, at the base of the Cambrian, the Champlainian (Middle Ordovician), the 
Pennsylvanian, the Gulfian (Upper Cretaceous), and the Pleistocene are scarred by 
erosion features with relief measured in tens or hundreds of feet. Valley systems, 
scarps, sink holes, and buried hills mark these unconformities. Although the sub- 
Grand Tower surface records the truncation and removal of several hundred feet of 
rock in some areas, no comparable erosion features have been noted. An exception 
might be a channel or valley in Morgan and Sangamon Counties that is suggested 
by scattered, thick, conglomerate sections (Whiting and Stevenson, 1965). Indi- 
rect evidence suggests that channels were cut 50 feet or more into Silurian and 
possibly Lower Devonian rocks during pre -Grand Tower erosion. 

The Silurian rocks in several areas covered by the Grand Tower contain a 
system of solution-enlarged joints, "fissures, " and cavities down to a depth of 
at least 70 feet. Many of these are filled by sand that is like the sand of the 
Dutch Creek but less well cemented, and by green or greenish gray clay that in 
places contains Middle Devonian fossils. The enlarged joint system resulted 
from pre -Grand Tower underground solution. Its wide extent suggests that during 
its development the water table lay some distance below the present top of the 
Silurian. This, in turn, requires that some master streams were incised as deeply 
as 50 to 70 feet beneath the general surface. Such stream valleys may have been 
overlooked because they occupy a minute fraction of the entire surface and wells 
have chanced not to hit them. On the other hand, the carbonates above and below 
the surface are so similar that some wells drilled through pre -Grand Tower valleys 
may have been misinterpreted. 

Beyond the limits of the Grand Tower, similar solution features beneath the 
unconformities that bevel the Lower Devonian, Silurian, and Ordovician strata have 
become filled by post-Grand Tower sediment of several ages. At the Marine oil 
field, in the northern part of T 4 N., R. 6 W., Madison County, the solution net- 
work was formerly considered to be post-Grand Tower, pre-Lingle (pre -Cedar Valley) 
(Lowenstam, 1948). However, much more extensive regional knowledge suggests 
that the sediment filling the cavities is of Grand Tower rather than Lingle age. 



GRAND TOWER LIMESTONE 21 



Although the Dutch Creek Sandstone Member is not present in the thin Grand Tower 
deposits over the Silurian reef at Marine, the sand in the cavity fillings is of the 
type found widely in the Dutch Creek. The clay in the cavities is not the eastern 
or Appalachia-derived mud that formed the shales of the Lingle but is essentially 
a locally derived insoluble residue of the Silurian and earlier limestones. Only a 
few pre-Lingle solution cavities have been found in the Grand Tower Limestone of 
the Marine area, where the cavities are unusually abundant in the Silurian. It is 
concluded, therefore, that the solution system at Marine, as elsewhere in the 
area covered by the Grand Tower, extends downward from the surface at the base 
of the Grand Tower rather than from that at the base of the Lingle. 



LITHOLOGY 

The Grand Tower Limestone is a carbonate unit within a much thicker car- 
bonate sequence, the Hunton Limestone Megagroup. In a broad sense, the forma- 
tions composing the megagroup are lithologically similar, with much duplication of 
specific rock types between the different units. Some rocks in the Grand Tower 
cannot be distinguished from some rocks in each of the other formations, but in 
its over-all characteristics, the Grand Tower can be set off as a sandy, nonsilty, 
nonargillaceous formation. It and the overlying Lingle Limestone include sandstone 
and sandy limestone, whereas sand in any form is rare in the rest of the Hunton 
and is unknown in some units. The Lingle is characterized, in addition, by in- 
cluding silty limestone, argillaceous limestone, and calcareous shale, which are 
essentially lacking in the Grand Tower. The Grand Tower shares its freedom from 
clay and silt with the Backbone Limestone and some Silurian units, but these are 
not sandy. 

All parts of the Grand Tower are thick bedded. Stylolites are fairly common 
but are widely spaced. They tend to be conspicuous with interpenetrating columns 
as much as several inches in length. 

The Grand Tower is characteristically fossiliferous limestone in the south- 
ern part of the state, dolomite in a belt crossing the south-central part, and un- 
fossiliferous or poorly fossiliferous lithographic limestone near the northern border 
in the central part (fig. 3). 

Limestone 

In the southern area, the limestone is generally rather light colored, vary- 
ing from light brownish gray and light grayish brown, buff, and tan, to almost white. 
The values are nearly all lighter than medium, and the hues are on the yellow or 
yellow-red side of neutral gray. Pink, red, or green tints occur rarely, if ever. 
The over-all color is lighter than that of most formations with which the Grand Tower 
is in contact. The Backbone Limestone and some Silurian rocks may be as light, 
but they tend to be partly pinkish or greenish. White chert is common in the Clear 
Creek, but the carbonate of the Clear Creek is generally darker than that of the 
Grand Tower in the southern region. 

Texturally the limestones of the southern region range from fine-grained 
micrite, both with and without scattered fossils, to coarse, fossil-hash calciru- 
dite. Entire fossils are probably commoner than fossil fragments, although beds 
of each occur. Oolites have not been found, and pelitic texture does not appear 
to be very common. The common fossil forms are crinoids, brachiopods, corals, 



22 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 

stromatoporoids, and bryozoans. The gastropod Platyceras is conspicuous in some 
cores, partly because its dark shell contrasts with the light color of most other 
constituents in the limestone. 

Lithographic limestone is uncommon in the southern limestone facie s, but 
it is the dominant and almost the only rock in the Cooper Limestone Member in 
central Illinois, immediately south of the Sangamon Arch. The rock is a pure, 
dense, nonporous micrite. Fossils are rare, but the few that occur are generally 
entire and include brachiopods, pelecypods, ostracods, and corals. In some lo- 
calities a small amount of clear calcite (sparite) fills irregular breaks in the litho- 
graphic rock or occupies tubular "bird's-eyes" one-half to three millimeters in 
diameter. Sand grains are scattered through the lithographic rock in some locali- 
ties, but elsewhere 10 to 40 feet or more of lithographic limestone contains very 
little sand and almost no other insoluble residue. 

Dolomite 

Between the two limestone regions is a belt in which the Grand Tower is 
almost exclusively dolomite. The area of interbedded dolomite and limestone be- 
tween the southern limestone facie s and the central dolomite belt is only a few 
miles wide and is represented on figure 3 by a single line. At the north, the con- 
tact between the dolomite facies and the lithographic limestone of the Cooper Mem- 
ber slants stratigraphically down to the north, so that a southward -thinning wedge 
of Cooper overlies a northward -thinning wedge of dolomite. The seguence within 
the dolomite belt and its relation to the southern limestone unit were described by 
Schwa.lb (1955). 

The most characteristic type of dolomite is confined to the Geneva Member, 
which is essentially the lower one-third of the dolomite in the central and southern 
part of the dolomite belt (fig. 5). This is a brown to dark brown, medium-grained, 
sucrosic, porous dolomite. The crystals are uniform in size. Porosity averages 
around 17 percent but ranges from about 12 to 2 5 percent. The very dark brown 
color is due to a small amount, no more than 1 percent, of organic matter that ap- 
pears as minute, floating, waxlike flakes when set free from the carbonate by acid. 
This flaky, floating residue is characteristic of dolomite from the Geneva. The 
Geneva is very nearly unfossiliferous; some cavities suggest poorly preserved fos- 
sil molds and a few chitinous microfossils— scolecodonts, chitinozoans, and charo- 
phytes— have been found. Preliminary examination has failed to reveal conodonts, 
although these are common in the limestone facies to the south. Except for the 
organic flakes, the insoluble residue of the Geneva consists almost entirely of the 
sand described later. 

The typical dark brown dolomite of the Geneva is overlain and grades lat- 
erally northward, and in some places southward, into a greater thickness of light- 
colored dolomite. These lighter dolomites are not formally named, but in Indiana 
they have been recognized informally as the "laminated beds" of the Jeffersonville. 
They constitute the bulk of the rock in the dolomite zone. 

The lighter colored, undifferentiated dolomites vary in color through gray, 
yellow, and tan. Occasional beds are almost as dark as the Geneva, but these 
lack the characteristic insoluble residue of the Geneva. The undifferentiated rocks 
are generally finer grained than the Geneva. They are laminated in part. The lam- 
inae consist of alternating layers of extremely fine and somewhat coarser crystalline 
dolomite. In some beds several feet thick the crystal size is fairly uniform, and 
in other beds larger crystals float in a matrix of extremely fine crystals. The 



GRAND TOWER LIMESTONE 23 

average porosity is less than in the Geneva, but the porosity is more variable. 
The argillaceous content is extremely low, and the rock resembles the Geneva in 
its sand content. Although there is a little interbedding of other types of dolomite 
with typical Geneva, in general the separation is sharp. The Geneva type cannot 
be distinguished from the other dolomites on most geophysical logs (fig. 5). 

Local zonation of the Grand Tower on the basis of relative abundance of 
fossil components and textural types is possible, as demonstrated by the zonation 
of the Jeffersonville in part of southern Indiana (Perkins, 1963). This kind of zon- 
ation cannot be extended across the entire basin. Concentrations of corals and 
stromatoporoids, for example, occur at several positions within the formation in 
different areas, although they are more common near the base. 

Chert 

Chert occurs sporadically in the Grand Tower, as it does in the overlying 
Lingle. No outstanding concentrations of chert, like those in the older Clear Creek 
and Bailey Formations, are present. Except at the extreme southern end of the 
state, chert is never more than about 1 percent of the Grand Tower, and in many 
wells no chert is noted. The chert occurs in irregular nodules. Vitreous as well 
as dull, opague varieties occur. Color ranges through gray, brownish gray, and 
brown and from very dark to light. The dense, white, opaque chert frequently seen 
in the underlying Clear Creek does not occur. 

Phosphate Nodules and Glauconite 

Glauconite is very rare. It goes unnoticed in most sample studies but is 
occasionally noted in insoluble residues. The Grand Tower has the least glauconite 
of any of the Devonian limestone formations. Phosphate is also very rare. Only 
a few small black phosphatic nodules have been seen, and there are no concentra- 
tions of phosphate comparable to those at the base of certain beds in the Lingle and 
in the Lingle correlatives in Indiana and Ohio. 

Sand 

By far the most characteristic and abundant noncarbonate constituent of the 
Grand Tower is quartz sand. Sand occurs in many parts of the formation in all con- 
centrations, from widely scattered individual grains to beds of sandstone several 
feet thick. The sand has undergone many cycles of erosion and deposition. It is, 
therefore, mature in the petrologic sense. Only the most stable heavy mineral 
suite— zircon, tourmaline, ilmenite, and leucoxene— is present. Where it is not 
affected by secondary enlargement, the sand in the Grand Tower is exceptionally 
well rounded. Both roundness and sphericity are particularly high in the large and 
medium size grades but decrease somewhat in the fine and very fine sizes. The 
larger grains also tend to be heavily frosted, whereas the smaller grains are more 
apt to be clear. Secondary crystal growth destroys the roundness of some quartz 
grains, but about 90 percent of the tourmaline grains, less subject to recrystalli- 
zation, are rounded (Potter and Pryor, 1961). 

Where the sand is concentrated in sandstone beds, its sorting is good. 
Where the sand is only a minor constituent of a limestone or dolomite, its sorting 
is much less perfect, and bimodal distributions are quite common. Payne (1942) 
illustrates such bimodal sand in an insoluble residue from the Grand Tower. 



24 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 

Sand is irregularly distributed, both geographically and stratigraphically. 
It tends to increase downward and westward, but with many exceptions. For ex- 
ample, sand is more abundant near the top of the formation in east-central Illinois 
and adjacent Indiana than it is farther south or directly west. Near the close of 
Grand Tower deposition, more sand may have come into the Illinois Basin from the 
Wisconsin Arch region than from the Ozarks, which provided most of the sand lower 
in the Grand Tower. 

Most concentrations of sand into sandstone beds more than a few inches 
thick are at the base of the formation in the Dutch Creek Sandstone Member. The 
Dutch Creek is not present everywhere, and in a few regions the basal beds of the 
Grand Tower are not even sandy. Moreover, the Dutch Creek is not present as a 
sandstone in all wells, even in those regions where it is best developed. Sand 
does not occur near the base of the Grand Tower in the outcrops at the western 
end of the Wittenberg Trough in Ste. Genevieve County, Missouri, in the subsur- 
face in and near Jefferson County, Illinois (fig. 3), or in the outcrops and shallow 
subsurface sections of the Jeffersonville in its type region near Louisville, Kentucky. 

The distribution of the Dutch Creek Sandstone within the dolomite region 
is imperfectly known. No basal sand is found in some wells. The sandstone is 
difficult to distinguish from the surrounding dolomite on geophysical logs, whereas 
its presence is at least suggested on many logs within the limestone region. More- 
over, sandstone is of no economic significance where it is overlain by porous, per- 
meable dolomite. As a result, many wells stop within the dolomite, and very few 
wells have been cored all the way through the dolomite into the sandstone. For 
these reasons, the basal sandstone was mapped only in the southern limestone 
facies (fig. 3) . 

The sand in the Grand Tower and Lingle Limestones is indistinguishable 
from the sand of the St. Peter Sandstone and other Ordovician and Cambrian sand- 
stones. During the Middle Devonian these formations were exposed on the Ozark 
and Wisconsin Arches. Sand that was eroded from the arches was carried eastward 
and incorporated into the Grand Tower and other Middle Devonian formations. 

The Dutch Creek Sandstone Member at any one point tends to be a very well 
sorted selection of the total population of available sand grains, better sorted than 
the scattered sand grains incorporated in beds that are mainly carbonate. Because 
of the general dominance of fine-grained sand, the Dutch Creek in most localities 
is a well sorted, fine-grained sandstone, so that the overlying carbonates contain 
some coarser grains, as was noted by Schwalb (19 55). However, at localities 
both in the outcrop and the subsurface, where the energy level was higher during 
deposition, the coarser sand grains were selectively retained, and the Dutch Creek 
at these localities is medium grained or medium to coarse grained. Preliminary 
studies of the Dutch Creek in Illinois and of similar Middle Devonian sandstones 
in Ohio, Indiana, and Kentucky suggested broad, simple patterns of size distribu- 
tion. However, additional data have shown that these patterns are extremely com- 
plex (Charles H. Summerson, personal communication). 

Except where it has been leached on the outcrop, the Dutch Creek every- 
where contains some carbonate and commonly is fossiliferous. In a few localities, 
a basal conglomerate consists of chert fragments from the immediately underlying 
formation. 

The porosity of the Dutch Creek varies widely. It is low where there is 
much carbonate cement. In some places in the dolomite belt where the Dutch Creek 
is only a few inches thick, it is a single tightly cemented quartzite bed of very low 



GRAND TOWER LIMESTONE 25 

porosity that fractures across rather than around the individual grains. This type 
of rock is not known in either of the limestone belts or in the thicker sections of 
Dutch Creek in the dolomite belt. In these situations, porosity reaches 15 or even 
20 percent and permeability is correspondingly high. 

GEOPHYSICAL CHARACTERISTICS 

The geophysical logs of the Grand Tower vary greatly from region to region 
(figs. 4, 5, and 6) Porosity is low in the limestone facies and moderate to high 
in the dolomite facies, so that the geophysical properties that are closely linked 
to porosity-electrical resistivity, neutron response, density, sonic velocity, and 
drilling time— are high in the limestone regions and low in the dolomite regions. 
Logs of these properties, which are normally plotted on the right-hand track, tend 
to be off-scale in the limestone regions and on-scale in the dolomite belt. Because 
of its very low clay content, the Grand Tower has extremely low natural gamma 
radioactivity and relatively high negative electrical self-potential. Logs of these 
properties, which are plotted on the left-hand track, are far to the left throughout 
the Grand Tower, except for a notch where the Tioga Bentonite Bed is thick enough 
to record (fig. 6) . 

A rough zonation of the formation in the southern limestone phase is possible 
on the basis of electrical resistivity (fig. 4). Where the fossiliferous limestone 
phase is more than 60 or 80 feet thick, most logs show three high resistivity zones, 
near the top, middle, and bottom of the formation, separated by two zones of mod- 
erate resistivity. These zones do not have sharp boundaries, but blend into each 
other, so that the resistivity curve through the Grand Tower resembles a sine curve 
of 2-| cycles. This resistivity zonation extends into Indiana and Kentucky but be- 
comes obscure as the section thins near the outcrop. However, the lowermost of 
the three high resistivity zones seems to drop out before the outcrop is reached. 
The slight increase in porosity responsible for the decreased resistivity of the 
intermediate zones is not evident on visual examination of either cuttings or cores. 
In a few wells, traces of chalky texture have been noted in these zones, but in 
most wells, there is no obvious differentiation. 

Within the dolomite region the Geneva can be picked in a few wells because 
it is slightly more porous and, therefore, has slightly lower resistivity than the 
overlying dolomites. However, this criterion must be used with caution, and in 
most wells the Geneva can be picked only by visual or even insoluble residue ex- 
amination of cuttings or cores. 

The Cooper Limestone Member is sharply differentiated from underlying 
dolomites by its high resistivity (fig. 5). 

The Dutch Creek Sandstone Member in the southern limestone area frequently 
can be differentiated from the overlying limestone by its lower resistivity. However, 
in most of this region, the underlying Clear Creek Limestone is partially dolomi- 
tized, and in places it is impossible on the basis of resistivity alone to tell the 
Dutch Creek from the Clear Creek. The sonic log in combination with a resistivity, 
neutron, or density log differentiates the Dutch Creek from rocks in the Clear Creek 
with similar porosity because the sonic velocity in quartz is appreciably lower than 
that in dolomite. 



26 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 

LITHOLOGIC DIFFERENTIATION OF THE GRAND TOWER 
FROM ADJACENT FORMATIONS 

Whereas the Grand Tower Limestone is virtually free of clay and fine silt, 
the overlying Lingle Limestone is markedly argillaceous. Most of the lithologic 
criteria that distinguish the two units are related to the increased clay and fine 
silt of the Lingle. Clastic particles in the Grand Tower were inherited from the 
early Paleozoic terranes of the Ozark and Wisconsin Arches and consist almost 
exclusively of sand grains. Mud from the rising Appalachia landmass to the east 
did not reach Illinois until Lingle time. Thus, the Lingle elastics include both 
western -derived sand and Appalachia-derived mud. 

The Lingle includes shale beds inches or feet thick, whereas shale streaks 
in the Grand Tower are no more than partings. The range of limestone types in the 
two formations is similar, except for the common occurrence of argillaceous vari- 
eties in the Lingle and their virtual absence in the Grand Tower. 

Lingle rocks are darker than the Grand Tower, but there is some overlap in 
this respect. The dark brown color of the Geneva Dolomite Member of the Grand 
Tower is due to organic rather than clay content and is an obvious exception to the 
general rule. The Grand Tower is thick bedded with widely spaced stylolites up 
to several inches in amplitude, whereas the Lingle is thin bedded with more numer- 
ous stylolitic partings of modest proportions. 

Dolomite is common in the Grand Tower but very rare in the Lingle. The 
purest phases of the Lingle are occasionally replaced by dolomite or dolomitic lime- 
stone, but in a broad area of central Illinois the Lingle-Grand Tower boundary can 
be placed with assurance at the top occurrence of dolomite. 

Chert is a minor constituent in both units but is relatively more abundant in 
the Lingle in western Illinois and in the Grand Tower in eastern Illinois. No vari- 
eties of chert seem characteristic of either unit. Oolites occur in the Lingle at two 
or three levels but have not been found in the Grand Tower. Phosphatic nodules 
and glauconite are moderately common in the Lingle but extremely rare in the Grand 
Tower . 

Beds of pure, lithographic limestone in the Lingle are particularly trouble- 
some because of their resemblance to the Cooper Limestone Member at the top of 
the Grand Tower in central and west-central Illinois. The two lithographic phases 
appear identical lithologically, so that the Lingle occurrences can be identified only 
because distinctive Lingle rocks lie beneath or lateral to them. In central Macoupin 
and Montgomery Counties, near the north border of figure 3, the lithographic zones 
in the Grand Tower and Lingle are 20 to 40 feet apart, but this interval narrows as 
the entire section thins northward toward the Sangamon Arch. A similar situation 
in central Missouri has led some authors to apply the term Cooper to lithographic 
limestones within the Callaway (Lingle equivalent). 

The fossils of the Grand Tower and Lingle differ specifically, but the same 
general types and even genera occur in both. The pteropod Tentaculites , a tiny 
ringed cone, is common in the Lingle and extremely rare in the Grand Tower. For 
practical purposes it may be used as an index to the Lingle. 

On geophysical logs the differentiation of Lingle from Grand Tower varies 
greatly from region to region. Except for the thin Tioga Bentonite Bed, the Grand 
Tower includes only rocks with high negative self -potential and very low radioac- 
tivity. Because of clay content, some beds of the Lingle have lowered self-poten- 
tial and increased gamma radiation. The electrical resistivity, neutron response 



GRAND TOWER LIMESTONE 11 

density, sonic velocity, and drilling time are influenced primarily by porosity and, 
therefore, are greatly affected by dolomitization. Where the Grand Tower is largely 
limestone these porosity-related properties tend to be higher in the Grand Tower 
than in the Lingle, whereas the situation is reversed in areas in which the Grand 
Tower is largely dolomite. Within the southern limestone facies of the Grand Tower, 
recognition of three zones of high resistivity in the Grand Tower is helpful because 
it permits placing of the Lingle-Grand Tower boundary on the electric logs on the 
resistivity slope just above the uppermost of these zones (fig. 4). 

Where post-Lingle rocks overlie the Grand Tower, they are so unlike the 
Grand Tower that their differentiation presents no problems. 

In general, the sand in the lower part of the Grand Tower serves to differ- 
entiate it from the older rocks on which it lies. However, in some localities sand 
is rare or lacking at the base of the Grand Tower. Moreover, in some types of 
well records the presence of sand is not indicated and this criterion cannot be 
applied. 

The Clear Creek Formation underlies the Grand Tower in part of central Illi- 
nois and in most of southern Illinois and adjacent parts of Indiana and Kentucky. 
The Clear Creek may generally be distinguished by greater abundance of chert, 
glauconite, and small black spheroidal fossil chitinozoans. Most beds in the 
Clear Creek are fairly cherty, and some are essentially solid chert. An opaque 
white variety characteristic of the Clear Creek has not been seen in the Grand Tow- 
er. Some of the less cherty beds in the Clear Creek are quite glauconitic. The 
most common chitinozoans are relatively large forms, the size of small to medium 
sand grains, and resemble miniature blueberries. The rare chitinozoans of the 
Grand Tower are unlike the common ones in the Clear Creek. Both faunas were 
described and illustrated by Collinson and Schwalb (1955). Doubly terminated 
quartz crystals of silt size are characteristic of some beds in the Clear Creek. 
The carbonate in the Clear Creek is generally darker than that in the Grand Tower. 
It is commonly dolomite or dolomitic limestone in much of the southern part of the 
state where the Grand Tower is entirely limestone. In that region the Clear Creek 
has lower electrical resistivity than the Grand Tower. On electric logs alone, the 
base of the limestone facies of the Grand Tower is sharp, but in places it is im- 
possible to tell whether a few feet of the Dutch Creek Sandstone Member underlie 
the limestone or whether the limestone rests directly on the Clear Creek. On sonic 
logs the Dutch Creek is represented by slow travel times that lie beneath the fast 
travel times of the limestones in the Grand Tower and above the moderate travel 
times of the underlying Clear Creek. 

The Backbone Limestone underlies the Clear Creek and should be present 
directly beneath the Grand Tower in a narrow belt north and west of the edge of 
the Clear Creek in central Illinois. However, this relation has been found in few, 
if any, wells. In several cross sections the Backbone appears to thin abruptly 
and perhaps disappear as it comes up to the pre-Grand Tower surface. The rela- 
tively pure limestone may have been leached during the development of the uncon- 
formity. The Backbone is a pure white or pink limestone that is dominantly crinoidal. 
In a few places a white crinoidal limestone in the Grand Tower is difficult to dis- 
tinguish from crinoidal beds in the Backbone. However, the Backbone is commonly 
glauconitic, and pink crinoidal limestone is common in the Backbone but extremely 
rare in the Grand Tower. 

The Bailey Limestone is much more silty, cherty, and darker colored than 
the Grand Tower, and it presents no difficulty in identification. Where it underlies 



28 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 

the dolomitic facies of the Grand Tower, the Bailey generally can be distinguished 
by a lower self-potential than the high negative self-potential of the Grand Tower. 

Many different varieties of Silurian rocks underlie the Grand Tower. Except 
for oil stains, shades of brown, tan, buff, and yellowish gray are practically non- 
existant in Silurian rocks and practically universal in the Grand Tower. When rocks 
that have been called white or gray are directly compared, a yellowish tint can nor- 
mally be distinguished in the Grand Tower and a greenish tint in the Silurian. Pink 
is also fairly common in the Silurian and extremely rare in the Grand Tower. The 
Silurian rocks that are strikingly glauconitic, cherty, silty, or argillaceous are 
readily distinguished from the Grand Tower. The chief problems arise in fine- to 
coarse-grained, white to gray, pure, dolomitic limestone or calcareous dolomite, 
particularly in the vicinity of the Sangamon Arch, where the Grand Tower is thin 
and may be absent in some wells, and where the Silurian rocks commonly are cut 
by crevices filled with Devonian sand. An unconformity representing 20 or 30 
million years separates the two units', but it is difficult to place the unconformity 
precisely in all wells. However, only a few feet of beds of questionable age are 
present between rocks definitely assigned to the Devonian and to the Silurian. 



PETROLEUM IN THE GRAND TOWER 

The Grand Tower Limestone is quarried in Ste. Genevieve County, Missouri, 
and was formerly quarried at Grand Tower, Illinois. However, there has been no 
active quarrying in Illinois for many years, and the Grand Tower is now of economic 
interest primarily as an oil reservoir. 

About 125 million barrels of oil have been produced from the Devonian rocks 
of Illinois. About 90 percent of the Devonian oil has come from the Grand Tower. 
The rest of the Devonian oil has come from sandstones in the Lingle and from cherty 
dolomitic limestone and dolomite in the upper part of the Clear Creek. Locally 
some oil has come from dolomite lenses in the Lingle, but Lingle carbonates are 
generally too argillaceous to serve as reservoirs. 

The most prolific of the Grand Tower reservoirs have been in the dolomites 
of the central dolomite belt and particularly in the Geneva Dolomite Member. The 
entire Devonian section was opened in many wells in such pools as Salem, Louden, 
and Centralia, but it is clear that the Geneva yielded much more oil than the rest. 
The Devonian production in Indiana is from the Geneva and also from overlying dolo- 
mite that is assigned to the Jeffersonville but equivalent to the post-Geneva dolo- 
mites in the Grand Tower of Illinois. The Geneva has provided the most prolific 
wells in Illinois, as much as 12,000 barrels in initial production and half a million 
barrels in cumulative production. The more important pools were discovered be- 
tween 1936 and 1941. Oil has been produced from the dolomites of the Grand Tower 
in stratigraphic traps, in normal deformational anticlines, and in domes formed by 
the draping of the Devonian strata over Silurian reefs. 

In more recent years the Dutch Creek Sandstone Member in the southern 
limestone area has been of great interest. Dutch Creek production is the deepest 
in the Illinois Basin (below 5000 feet) and has been very prolific, although only 
two relatively small pools have been discovered. The first of these, in Aden Con- 
solidated field, sees. 16 and 17, T. 3 S., R. 7 E., Wayne County, was discovered 
in December 1959, when Texaco No. 16 Silverman was completed in the Dutch Creek 
at 5325 feet for a prorated initial production of 207 barrels. The well has remained 
a flowing well, and at the end of 1964 had produced about 350, 000 barrels of oil 
with no brine (fig. 7). It is prorated by the operator to a little more than 150 barrels 



GRAND TOWER LIMESTONE 



29 



900 



800 



700 



600 



500 



400 



300 



200 



Gas - Oil 

Ratio 

Cu. Ft./Bbl 

- 1500 - 



TEXACO INC No. 16 SILVERMAN 

SW NW I6-3S-7E, WAYNE CO. 

ADEN POOL 



Devonian (Dutch Creek) 




1964 



Barrels 
of Oil 



400,000 



350,000 



300,000 



250, 000 



200,000 



150,000 



100,000 



50, 000 



-•-5,000 



Figure 7 - Production history of Texaco Inc. No. 16 Silverman, Aden pool, the 

discovery well of Dutch Creek oil in the deep part of the Illinois Basin. 



30 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 

per day. The oil is 41.5 degrees API gravity, and the produced gas-oil ratio has 
averaged 9 00 cubic feet per barrel. The well is the most valuable in the state. 
A well a quarter of a mile to the north, No. 3 Silverman, was deepened to the Dutch 
Creek and has produced about half as much oil. It is now pumping oil with brine 
of 122, 000 parts per million chlorinity and 209, 000 parts per million total dissolved 
solids. A third well has produced a small amount of Devonian oil in a common 
completion with Mississippian pay zones. 

About 12 miles to the east, Dutch Creek production has been found in sees. 
28, 29, 32, and 33, T. 2 S., R. 9 E., Goldengate Consolidated field, Wayne Coun- 
ty. The discovery well was Collins Brothers No. 1 Wood "A, " in the NE{ NE| NE^ 
sec. 32, completed in August 1961. The well flowed 270 barrels of 39.4 degrees 
API oil from 53 50 feet. Of 16 wells completed in this pool, 6 or 7 have accounted 
for most of the production, and these were generally completed at higher initial 
production, up to 840 barrels per day. None now flow. Gas-oil ratios have aver- 
aged about 1900 cubic feet per barrel. The produced brine, which ranges in chlo- 
rinity from 124,000 to 126,000 parts per million, and in total dissolved solids from 
210,000 to 216,000 parts per million, is the most concentrated brine produced in 
the state. 

The search for Dutch Creek production in the surrounding areas of Wayne, 
Hamilton, White, and Edwards Counties has been unsuccessful. Nearly all signi- 
ficant closures mapped on Mississippian horizons have been penetrated by at least 
one test. In about half of these the Dutch Creek has been tight, or represented 
by sandy limestone, but many have found permeable sandstone sections with brine. 
Some of the wells with brine have been on structures with much greater closures 
than the two structures that produced oil. 

Despite the disappointing record since the discovery of the pools at Aden and 
Goldengate, the Dutch Creek offers the possibility for production over a consider- 
able area. In the fault-line pools of the Wabash Valley fault complex, shows in 
the Dutch Creek were in sections too tight to be productive. In addition, Dutch 
Creek shows have been found in some wells in the extreme southern part of the 
state, south of the region that now produces in the Mississippian rocks. The Dutch 
Creek Sandstone must be considered a potential drilling target in part or all of the 
counties of extreme southern Illinois. 



GRAND TOWER LIMESTONE 31 

APPENDIX 
WELLS USED IN CROSS SECTIONS (FIGS. 4-6) 

1. Obering No. 1 Hasemeier, NW SW 10-2S-2W, Washington County 

2. National Associated Petroleum No. 1 Norma R. Jack et al. Comm., SE SE 

19-2S-1W, Washington County 

3. Ohio Oil No. 1 Sawyer et al., SW NW 33-2S-1W, Washington County 

4. Ohio Oil No. 1 Lamczyk, NE NE 23-3S-1W, Washington County 

5. Magnolia Petroleum No. 9 Eubanks-Winesburgh, SE SE 35-2S-1E, Jefferson 

County 

6. Magnolia Petroleum No. 1 Jones, NE NE 10-3S-2E, Jefferson County 

7. Athene Development No. 1 Williford-Bosworth Comm., SE NE 10-3S-3E, 

Jefferson County 

8. Sun Oil No. 1 Aydt, SE SW 1-4S-4E, Jefferson County 

9. Athene Development No. 1 Scrivner, Nj S| 27-3S-5E, Hamilton County 

10. Texaco No. 1 Draper, NW SW 8-3S-6E, Wayne County 

11. Texaco No. 3 Silverman, NW NW 16-3S-7E, Wayne County 

12. Nation Oil No. 2 W. P. Mcintosh, NE SW 31-3S-8E, White County 

13. Toto Gas No. 1 E. J. Winter, NW NE 36-4S-9E, White County 

14. Phillips Petroleum No. 1 Garr, NW NW 31-4S-11E, White County 

15. Superior No. C-17 H. C. Ford, SW SE 27-4S-14W, White County 

16. Indiana Farm Bureau No. 1 Rowe, SE NE 36-5S-13W, Posey County, Indiana 

17. Carter No. 13 Culver heirs, SW SW 24-P-21, Union County, Kentucky 

18. Joe Simpkins No. 1 Pointer, NW SW 18-8N-8W, Macoupin County 

19. Glen Bryant No. 1 Menke, NE SW 12-7N-7W, Macoupin County 

20. Stewart Producer's No. 1 Griffith, SW SW 34-7N-5W, Montgomery County 

21. Stewart Producer's No. A-l Donk Bros. Coal, NE NW 33-6N-4W, Bond County 

22. W. L. Belden No. 1 John Anthony, NE NW 28-6N-2W, Bond County 

23. Thomas Doran No. 1 Baumann-Weaver, SE NW 2-5N-1W, Fayette County 

24. Kewanee Oil No. 1 Gehle, SE NE 13-5N-2E, Fayette County 

25. National Associated Petroleum No. 5 Ed Lacey et al., NW NE 21-4N-4E, 

Marion County 

26. Texaco No. 7 Allen "A," NE NE 36-3N-5E, Clay County 

27. Texaco No. 1 Greathouse, SE NW 27-1N-6E, Wayne County 

28. Texaco No. 5 H. O. Fuhrer NCT-1, SW SE 28-1S-6E, Wayne County 

29. Peake Petroleum No. 1 Feathers, SE NW 14-2S-6E, Wayne County 

30. Humble No. 33 Busiek-Crawford, SE NE 11-8S-10E, Gallatin County 

31. Superior No. 1 P. Bra selton Comm. , SW SE 24-2S-12W, Gibson County, 

Indiana 

32 . E. Paul DuPont, Jr. No. 1 Schafer, NW NE 31-2N-11W, Wabash County 

33. Bell Brothers No. 1 Wampler, SE NE 27-5N-11W, Lawrence County 



32 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 



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Hallstein, W. W., 1952, Insoluble residues of the Grand Tower Limestone: Univ. 
Illinois (Urbana) unpublished M.A. thesis. 



GRAND TOWER LIMESTONE 33 

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34 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 389 

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Illinois State Geological Survey Circular 389 
34 p., 7 figs., app., 1965 



Printed by Authority of State of Illinois, Ch . 127, IRS, Par. 58.25. 



CIRCULAR 389 

ILLINOIS STATE GEOLOGICAL SURVEY 

URBANA